The invention relates to devices for delivering, injecting, infusing, administering or dispensing a substance, and to methods of making and using such devices. More particularly, it relates to an injection device, such as an auto-injector, for injecting a fluid product, such as a drug for diabetes or insulin therapy, wherein, after the product has been successfully administered, a needle protecting sleeve associated with the injection device is moved or slid over the injection needle to protect against injury.
Moving or sliding a needle protecting sleeve over a needle in the distal (forward) direction, from its proximal (rearward) position in which the needle is exposed, by using a spring, such that the needle is protected against being accessed from without, is known from the prior art. The spring which charges the needle protection with a spring force is biased by an amount in the proximal position of the needle protecting sleeve. When the needle protecting sleeve is advanced beyond the injection needle, the spring force decreases according to the rules of Hooke's Law. The bias on the spring therefore has to be selected such that the needle protecting sleeve can reliably assume the end position in which it covers the injection needle.
Shifting the needle protecting sleeve from a distal position into the proximal position beforehand, to bias the spring, is also known. During this movement, mechanical switching processes of parts which are coupled to the needle protecting sleeve are performed as applicable. To effect these switching processes, additional forces which act on the needle protecting sleeve in the proximal direction are needed, in addition to the force needed to bias the spring, to shift the needle protecting sleeve in the proximal direction. It is, however, desirable to keep the total force needed to shift the needle protecting sleeve in the proximal direction low, to make it easier for the user to handle the device. On the other hand, as stated above, increased spring forces are desirable for shifting the needle protecting sleeve in the distal direction from the proximal position.